Photographic developer



United States Patent 3,022,168 PHOTOGRAPHIC DEVELOPER Oskar N. Stjiirnkvist, Orebro, Sweden, assignor to Akhebolaget Pharmacist, Uppsala, Sweden No Drawing. Filed June 24, 1959, Ser. No. 822,443 Claims priority, application Sweden June 28, 1958 14 Claims. (Cl. 96-66) This invention relates to a photographic developer containing ascorbic acid as a developing agent and, more particularly, to a new developing solution of high developing capa ity containing ascorbic acid as an active developing agent within the pH range of from about 8 to 9.

The addition of ascorbic acid has been previously suggested as an antioxidant to sulphite-free tanning developers as well as sulphite-containing, non-tanning developers. Hereby it has been found that the ascorbic acid more or less retards the aerial oxidation of the developer and also that it may be more active in this respect than a corresponding amount of sulphite in connection with the use of pyrocatechol-, pyrogalloland hydroquinone developers.

It is also known that under certain conditions ascorbic acid may act as a developing agent. However, this eliect is not obtained with the ascorbic acid alone but it appears only in the presence of an alkali-carbonate or alkali hydroxide at pH-values of about 10 and more from which it is evident that the ascorbic acid has a low reduction potentialand results in an image with a very strong formation of fog, strong blackening and finally over-blackening. Such a developer is therefore of no value for practical purposes.

According to the present invention it has been found that it is possible to activate the ascorbic acid with certain conventional developers, so that its low reduction potential is increased and its activity as a photographic developer appears already at lower pH-values at which the ascorbic acid alone is photochemically inactive or only gives a faint fog or extremely faint image traces. In this process, these activating developers have the double function of developing agents and activating agents for the ascorbic acid. It has proved that in this manner developing compositions can be obtained that not only give as good results as the best known developers but are also in several respects essentially superior to them.

Based on these observations, one essential feature of the present invention resides therein that the new photographic developer according to the invention comprises ascorbic acid in combination with such activating developers which are capable to imparting to the ascorbic acid high developing properties within the pH-range of from about 8 to 9.

In this connection it may be mentioned that the term ascorbic acid used in the present specification and in the appended claims is intended to comprise all different forms of ascorbic acid, for example l-ascorbic acid, d-ascorbic acid and iso-ascorbic acids.

With this developer images are obtained which-with respect to fine grain, definition, correct gradation and compensation of exposure-entirely correspond to the best results that can be obtained with existing first-class developers. Moreover, these developing compositions according to the invention have a stability and a durability not previously attained, and which can be used without regeneration with excellent results for developing a much larger area per volume unit solution than is possible with a developer without the addition of ascorbic acid.

As activators for the ascorbic acid, developing agents 3,022,168 Patented Feb. 20, 1962 or systems of developing agents having an essentially higher reduction potential than the ascorbic acid itself can be used. As preferred examples of activators may especially be mentioned monomethyl-p-aminophenol sulfate (Metol) and monomethyl-p-aminophenol sulfatehydroquinone (Metol-hydroquinone), both of which have an excellent effect. Hydroquinone alone has no activating effect, as its reduction potential differs too little from that of the ascorbic acid. A further example of a suitable activating agent is phenylpyrazolidone.

An essential condition for the activation of the ascorbic acid and the provision of a developer having the stated properties is that the pH-value of the developer should be within the said limits of 8 to 9. This is evident from the comparative tests described below, which have been carried out with a Metol-hydroquinone developer in the one case with, and in the other case without, addition of ascorbic acid and with the use of test films (DIN 19) of the same motif exposed for exactly the same time period and under the same conditions in other respects.

As a norm for judgment may be taken the conventional fine grain and compensating developer used in the negative process and having the standard compo sition: 2 g. Mctol, 4 g. hydroquinone, g. dry sodium sulphite and '2 g. borax per liter developing solution. At 20 C. this developer has a pH-value of 8.6 and the developing time, which of course varies according to the negative material, is on an average 10 minutes.

For the experiment was prepared a developing solution containing only a tenth of the developing agents of this standard solution, i.e. 0.2 g. Metal and 0.4 g. hydroquinone per liter, but with the concentrations of the other agents unchanged. One of the test films was developed for 10 minutes. The negative thus obtained was, as expected, very thin and under-developed. The

pictorial values were satisfactory, but the gamma value was particularly low.

A new developing solution of exactly the same composition was prepared, and ascorbic acid was added in an amount corresponding to 10 g. per liter. The pH-value of this solution was adjusted to 8.5 by the addition of potassium hydroxide. A test-film of the same kind as before was then developed with this solution for 10 minutes. The negative thus obtained was quite normal, with correct graduation, definition, gamma value and tine gram.

This difference in the results obtained in the two experiments is to he'ascribed to the activation of the ascorbic acid. With ascorbic acid alone-i.e. without addition of Metol-hydroquinoneand under otherwise the same conditions, only scarcely observable faint fogs were obtained.

Further experiments were then carried out with the same Metol-bydroqiunone-ascorbic acid developer, which was buffered by the addition of potassium pyrosulphite to lower and lower pH-values, whereby' the activation of the ascorbic acid decreased more and more, and finally ceased altogether when the pH sank below 8.

in a similar way, experiments were carried out with a Metol developer having a low concentration of Mctol, 0.75 g. Metol per liter, corresponding to only a tenth of that of the standard developer, at a pl-l-value which had been buttered down to 7.7 by the addition of pyro sulphite. The result was very thin, highly underdeveloped negatives. The addition of ascorbic acid, which had been neutralized with potassium hydroxide, in an amount of 10 g. per liter developing solution did not result in any noteworthy change in the developing result. However, when the pH-value of the ascorbic acid-containing solution was increased to 8, completely normal negatives were obtained, and also in this case it was found that the best result was obtained at a pH of about 8.5.

I 3 to 15. g'. per liter developing solution. portions between ascorbic acid and the other developing From the afore-said experiments it is evident that the lower limit of the pH interval for the occurrence of the activation effect is at about 8. Optimal results are obtained at pH-values of 8.5-8.6. At higher pH-values the activation efiect decreases and the limit value pH=9 should not be exceeded, since in this case the developer will give less satisfactory results in certain respects, particularly regarding the gradation.

From the experiments it is further evident that only a very low concentration of the activating developing agent is necessary to effect the activation. Thus, it has proved that in case of activation with Metol-hydroquinone even a concentration thereof amounting to 5% of that of the standard developer is sufficient to obtain activation, though in this case the developing time has to be extended. However, in order to prevent a decrease of activation with repeated use of the solution, the content of activating agent should be made higher.

The content of the ascorbic acid in the developing solution may preferably be within the range of from about Suitable proagent also serving as activator are, in case of activating ascorbic acid with Metol, for example 0.5-7.5 g. Metoland 5-15 g. ascorbic acid per liter developing solution and, in case of activating ascorbic acid with Metol-hydroquinone, 1-3 g. Metol, 1-5 g. hydroquinone and 3-15 g. ascorbic acid per liter. When using phenylpyrazolidone as an activator, 0.05-0.4 g. l-phenyl-S-pyrazolidone and 3-15 g. ascorbic acid per liter are suitable proportions.

Further, the developer contains additions of usual components in developing compositions, i.e. alkali sulphite or bisulphite as reduction agents, borax or borate as buffering agents, alkali carbonate or alkali hydroxide etc. The total concentration of the developing agents in the developer may be essentially higher than in the usual standard developers, whereby the capacity of the developer is essentially increased.

As a rule, these known standard developers may be used for the development of or at most film rolls per'liter solution with completely good results, i.e. without any defects in gradation, but in this case it has generally been necessary to extend the development time by about 100%. By regenerating the solution this number of rolls may be increased, although hardly to more than 25 film rolls without impairing the quality of the negative.

With the ascorbic acid-containing developer according to the invention it is possible to give the developing agents in the solution such a concentration that 40-45 film rolls or even more may be developed per liter developing solution. However, it has been found that this great capacity of the developer can hardly be utilized with completely good results with only borax buffering. Continued use of the developing solution results in a gradual de crease of the pH-value which may, of course, be compensated by the addition of more borax to the solution,

. but this maylresult in certain disturbances. Consequently,

borax alone does not give a sufliciently stable buffer system for the maintenance of a sufficiently constant pH value with the-pH range of about 8 to 9 during the whole period for optimal utilization of the capacity of the developer, which is a condition for the uniform function of the developer.

In order to achieve this result without having recourse to renewals of the solution by the addition of alkali, the new developer composition according to the invention as a second essential feature comprises a buffer system con- This buffer system functions in such a way that the boric acid which is formed when the borax undergoes hydrolysis in the developer forms monobasic complex acids with the alcohols in question, the said acids being stronger than the boric acid, whereby the pH-value of the borax hydrolysis decreases. In other words, the increase of the pH-value in which the hydrolysis of the borax would otherwise result is eliminated. In this way it is possible from the outset to add to the developing system a sufficient amount of borax and a suitable amount of the said polyhydric alcohol, so that the pH-values of the solution can be varied within certain limits and then be maintained practically constant as long as the solution is in use.

In view of the foregoing, the present invention relates to a photographic developer consisting of an alkaline so lution comprising ascorbic acid as an active developing agent, an activator consisting of a developing agent of higher reduction potential capable of imparting to the ascorbic acid high developing properties within the pH range ofabout 8 to 9, and a buffer system consisting of borax in combination with an aliphatic polyhydric alcohol having at least two adjacent hydroxyl groups in the cis position, said polyhydric alcohol being capable of forming with the boric acid complex acids which are stronger than the boric acid, the pH of said developing solution being within the range of from about 8 to 9.

As indicated above, the content of ascorbic acid, preferably l-ascorbic acid, in the same developing solution may suitably be within the range of 3-15 g. per liter solution. The content of activator may vary within vwide limits, for example from 0.05 g. to 7.5 or 8 g. per liter, dependent on the nature of the accelerator. Suitable proportions of borax and the above-mentioned aliphatic alcohol in the buffer system are about 10-30 g. borax and about 5-100 g. glycerol, or 5-30 g. mannitol, or 10-50 g. sorbitol, per liter developing solution, and a suitable content of sodium sulphite is 40-100 g.'of the anhydrous compound per liter solution.

With this ascorbic acid-strengthened developer with its novel buffer system, 40-50 film rolls (DIN 19) can be developed per liter developing solution with entirely good results and without any regeneration of the solution being necessary. The developing time with this developer is essentially shorter than with the corresponding ascorbic acid-free developer adjusted to the same pH-value. Particularly noteworthy is the fact that when developing such a great number of films the developing time remains practically constant, and need only be extended by about 10 percent after the developing of about 20 rolls. The developing time is also to a large extent independent of the exposure time, and the developer has a great compensation ability in case of incorrect exposures. Particularly the ability to bring out details from shaded parts without over-blackening the light parts in strongly under-exposed negatives is excellent. Furthermore, films having the most widely difiering degrees of sensitivity can be developed with this developer with good results.

As already stated above, the composition of the developer according to the invention may be varied within broad limits. As more specific examples of the composition the following may be mentioned:

Example 1 A developing solution was prepared containing the following components:

This developer had the pH value 8.5. The developing time for a certain film was 3.5 min. and for the same film with the same developer without the addition of neutralized ascorbic acid 10 min. which shows the strong activating etiect of the small addition of Metol.

Example 2 A developing solution was prepared containing the following components:

G. Metol 7.5 l-Ascorbic acid 10.5 Sodium sulphite, dry 100 Borax 15- Potassium hydroxide 6 Glycerol 70 Water to 1 liter.

This developer had the pH value of 8. The developing time was about 2.5 min. The solution could be used for developing 50 film rolls.

For the same developer without the addition of neutralized ascorbic acid the developing time was 3 min. However, with continued use of the solution the ditierences in developing time became much greater.

Example 3 A developing solution was prepared containing the fol- The pH value was 8.5 and the developing time 4 to 5 min., without neutralized ascorbic acid to 12 min. The solution could be used for developing 50 film rolls.

The same result may be obtained by replacing the glycerol content with 9 g. of mannitol.

Example 4 A developing solution was prepared containing the following components:

G. ibphenyl-B-pyrazolidone 0.20 l-Ascorbic acid 10 Sodium sulphite, dry 40 Borax 15 Potassium hydroxide 3.8 Glycerol Water to 1 liter.

'Ihissolution had the pH value 8.5. The developing time was 2.5 min., without neutralized ascorbic acid min. The solution could be used for developing 25 film rolls.

In all these examples panchromatic film (DIN 19) was used and the development was carried out at a temperature of 20 C.

In addition to the valuable properties already described, the novel developer according to the invention has, as already previously indicated, also the very important advantage of being highly stable.

In general the standard developers on the market are stated to be stable for 8 to =10 weeks after the first developing, provided that they are stored in bottles filled to the top. The developer according to the invention has been tested for a period of 4 months wtih regard to its resistance to auto-oxidation, during which period 45 film rolls were developed in a 1 liter bottle, the development volume of which decreased to 400 ml. in the period. In the experiments the developer was poured into and out of the storage bottle an equal number of times and the volume of air in the bottle was increased and partially renewed on each occasion. In this connection there was no refilling into a smaller bottle to diminish the cushion of air. The developing was in one series carried out in an open bowl in which in connection with the passage of the film through the liquid the atmosphere was allowed to act freely thereon, and in another series in a developing tank in which air was sucked down into the liquid during the continuous rotation of the filling tube of the tank. In spite of this the effect of the developer remained constant which shows it excellent stability and storing properties.

Regarding the exact function of the ascorbic acid in the developing process and the inner electrochemical interaction with the other developing agents and the processes of reaction occurring therein, no definite explanation can be given, as the invention is the result of experimental work. However, it is probable that a reduction system with a great potential is formed which is nevertheless able to work economically and restrictively in the photographic reduction and perhaps successively.

with the difierent components. In this system it must be assumed that the ascorbic acid is protected in some way against auto oxidation in view of the great stability of the developer. Possibly the trilogy Metol-hydroquinonesulphite functions as an oxidation protector.

The developers activated with ascorbic acid according to the invention may be used in the same photographic developing processes and together with the same photographic emulsion material as corresponding developers without addition of ascorbic acid. The invention is in the foregoing described especially in connection with negative developing and the developer has its most important 4 application for this purpose, but it may also be used for developing positives.

What I claim is:

l. A photographic developer, comprising an alkaline solution containing ascorbic acid as an active developing agent an activator having a higher reduction potential than ascorbic acid capable of imparting to the ascorbic acid high developing properties within the pH range of from about 8 to 9, and a butier system consisting of borax in combination with an aliphatic polyhydric alcohol having at least two adjacent hydroxyl groups in the cis position, said polyhydric alcohol being capable of reacting with the boric acid fromed from the borax by hydrolysis with the formation of complex acids which are stronger than the boric acid, the pH of said developing solution being within the range of from about 8 to 9.

2. A photographic developer of high developing capacity, comprising an alkaline sloution containing ascorbic acid as an active developing agent, an activator having a higher reduction potential than ascorbic acid capable of imparting tothe ascorbic acid high developing properties within the pH range of from about 8 to 9, said activator being selected from the group consisting of monomethyl-p-aminophenol sulfate, monomethyl-paminophenol sulfate-hydroquinone and phenylpyrazolidone developers, and a buffer system consisting of borax in combination with an aliphatic polyhydric alcohol having at least two adjacent hydroxyl groups in the cis position, said polyhydric alcohol being capable of reacting bic acid as an active ing at least two adjacent hydroxyl ti'o'n. being wherein the said aliphatic polyhydric alcohol is mannitol.

8. A photography developer as claimed in claim 2, wherein the said aliphatic polyhydric alcohol is sorbitol.

9. A photographic developer of high developing capacity, comprising an alkaline solution containing ascordeveloping agent in an amount of from about 3 to 15 g. per liter developingsolution, an activator having a higher reduction potential than ascorbic acid capable of imparting to the ascorbic acid high developing properties within the pH range of from about 8 to 9, said accelerator being selected from the group consisting of monomethyl-p-aminophenol sulfate, mono- 'methyl-p-aminophencl sulfate-hydroquinone and 1- phenyl-3-pyrazolidone' developers and being present in an amount of from 0.05 to 8 g. per liter solution, and a bufier system comprising from about 10 to 30 g. bor'ax in combination with an aliphatic polyhydric alcohol havgroups in the cis position, in anamount of .from about 5 to 100 g. per liter solution, said polyhydric alcohol being capable of reacting with the boric acid formed from the borax by hydrolysis with the-formation of complex acids which are stronger than the'boric' acid, the pH of the said developing soluwithin the range of from about 8 to 9.

developer of high developing capacity, comprising an alkaline solution containing per liter developing solution from about 5 to 15 g. l-ascorbic acid, from about 0.5 to 7 g. of monomethyl-p-aminophenol sulfate,'from-about 40-100 g. of anhydrous sodium sulphite, from about to 30 g. borax and from about 5 to 100 g. of glycerol, the pH of said developing solution being within the range of from about 8 to 9.

11. A photographic developer of high developing capacity, comprising an alkaline solution containing per 10. A photographic developing solution from about 3 to g. of l-ascor his acid, from about 1 to 3 g. of monomethyl-p-aminophenol sulfate, from about 1 to 5 g. of hydroquinone, from about 40 to 100 g. of anhydrous sodium sulphite, from about 10 to 30 g. borax and from about 5 to 100 g. of glycerol, the pH of the said developing solution being within the range of from about 8 to 9.

12. A photographic developer of high developing capacity, comprising an alkaline solution containing per liter developing solution from about 3 to 15 g. of l-ascorbic acid, from about 0.05 to 0.4 g. of l-phenyl-S-pyrazolidone, from about 40 to 100 g. of anhydrous sodium sulphite, from about 10-30 g. borax and from about 5 to 100 g. of glycerol, the pH of the said developing solution being within the range of from about 8 to 9'.

13. A photographic developer of high developing capacity, comprising an alkaline solution containing per liter developing solution from about 3 to 15 g. of l-ascorbic acid, from about 1 to 3 g. of mcnomethyl-paminophenol sulfate, 'from about 1 to 5 g. of hydroquinone, from about 40 to 100 g. of anhydrous sodium sulphite, from about 10 to 30 g. borax and from about 5 to 30 g. of mannitol, the pH of the said developing solution being within the range of from about 8 to 9.

14. A photographic developer of high developing capacity, comprising an alkaline solution containing per liter developing solution from about 3 to 15 g. of l-ascorbic acid, from about 1 to 3 g. of mono'methyl-p-aminophenol sulfate, from about 1 to 5 g. of hydroquinone, from about 40 to 100 g. of anhydrous sodium sulphite, from about 10 to 30 g. borax and from about 10 to g. of sorbitol, the pH of the said developing solution being within the range of from about 8 to 9.

References Cited in the file of this patent UNITED STATES PATENTS James et al. Sept. 7, 1954 OTHER REFERENCES 

2. A PHOTOGRAPHIC DEVELOPER OF HIGH DEVELOPING CAPACITY, COMPRISING A ALKALINE SOLUTION CONTAINING ASCORBIC ACID AS AN ACTIVE DEVELOPING AGENT, AN ACTIVATOR HAVING A HIGHER REDUCTION POTENTIAL THAN ASCORBIC ACID CAPABLE OF IMPARTING TO THE ASCORBIC ACID HIGH DEVELOPING PROPERTIES WITHIN THE PH RANGE OF FROM ABOUT 8 TO 9, SAID ACTIVATOR BEING SELECTED FROM THE GROUP CONSISTING OF MONOMETHYL-P-AMINOPHENOL SULFATE, MONOMETHYL-PAMINOPHENOL SULFATE-HYDROQUINONE AND PHENYLPYRAZOLIDONE DEVELOPERS, AND A BUFFER SYSTEM CONSISTIG OF BORAX IN COMBINATION WITH AN ALIPHATIC POLYHYDRIC ALCOHOL HAVING AT LEAST TWO ADJACENT HYDROXYL GROUPS IN THE CIS POSITION, SAID POLYHYDRIC ALCOHOL BEING CAPABLE OF REACTING WITH THE BORIC ACID FORMED FORM TEH BOROX BY HYDROLSIS WITH THE FORMATION OF COMPLEX ACIDS WHLCH ARE STRONGER THAN THE BORIC ACID, THE PH OF THE SAID DEVELOPING SOLUTION BEING WITHIN THE RANGE OF FROM ABOUT 8 TO
 9. 